This invention relates to communication systems, including but not limited to indicating unusable sites in a communication system to communication units.
Wide-area dispatch communication systems are known. Commercial examples of such systems include SMARTZONE(trademark) and OMNILINK(trademark) systems available from Motorola, Inc. In these systems, multiple base sites are geographically distributed over a wide-area to provide over-the-air communications for communication units (e.g., transmit-only, receive-only, and receive and transmit units; vehicle-mounted or portable communication units, such as in a land mobile system, and communication unit/telephones in a cellular system) travelling in the area. The base sites are connected via a communication path to a zone controller that performs call control and mobility management for communication units and talkgroups in the system. Each site provides one or more communication resources, including RF resources such as narrow band frequency modulated communication resources, time division multiplex slots, frequency pairs, and so forth. A zone manager is operably coupled to the zone controller in the system to configure system parameters, physical device configuration, and communication unit, and talkgroup attributes. Talkgroups are groupings of communication units that wish to intercommunicate.
In existing wide-area dispatch systems, a base site may be unusable for a communication unit or a talkgroup for various reasons. A site may be marked as unusable for a communication unit or talkgroup to reduce the call traffic load at the site. A site may be marked as unusable by entering unusable site configuration information at the zone manager. The zone manager then passes the configuration information to the zone controller that keeps track of usable site information for both communication units and talkgroups. Marking a site unusable makes the site immediately unusable by the affected communication units and talkgroups.
If a site is marked unusable for a communication unit, the communication unit is unable to participate in any individual services such as private calls (non-talkgroup) or telephone interconnect calls. While a site is marked as unusable for a particular talkgroup, calls involving that talkgroup are not allowed at that site. For example, if a talkgroup call request is received from the unusable site, the request will be denied by the zone controller. Similarly, if a talkgroup call is granted from another site involving the talkgroup, the unusable site will not receive the audio associated with the call. If a communication unit roams into an unusable site and attempts to register, its registration request will be denied and the communication unit is given a message to leave the site, thereby preventing the communication unit from registering at a site that is unusable.
Unfortunately, a communication unit is not notified when a site is made unusable, even if the communication unit is presently registered at the unusable site. A communication unit is made aware that it is at an unusable site only indirectly in response to actions taken by the communication unit. For example, if the communication unit attempts a call at the unusable site, then the communication unit, in response to being denied, will first attempt to find a usable site. Also, the communication unit may roam from an unusable site to a usable site as a part of normal mobility. These methods of changing to a usable site from an unusable site are sporadic and can cause a communication unit to unknowingly miss calls while registered at an unusable site.
Accordingly, there is a need for a method to notify communication units of an unusable site so that units can select a usable site to prevent the communication unit from missing calls.